Stabilizing methyl-substituted polysiloxanes



Patented Mar. 9, 1948 STABIIJZING METHYL-SUBSTITUTED POLYSILOXANES Charles A. Burkhard, Alplaus, and Winton I. Patnode, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York No Drawing. Application September 28, 1946, 1

Serial No. 700,154

3 Claims.

The present invention relates to compositions of matter comprising methyl-substituted polysiloxanes which exhibit good resistance to gelation at elevated temperatures, and methods of preparing the same. More particularly, the invention is concerned with g. method of retarding gelation at elevated temperatures, for example, at 200 0., of a liquid composition comprising a methyl polysiloxane containing approximately two methyl groups per silicon atom, which method comprises incorporating and intimately dispersing in the said polysiloxane small amounts of ketene (CzHzO).

The liquid methyl polysiloxanes stabilized in accordance with the practice of our invention are prepared, for example, by hydrolyzing a dimethyl-substituted dihalogenosilane, for instance, dimethyl dichlorosilane, as illustrated. e. g., by the method disclosed and claimed in Patnode application Serial No. 463,813, filed October 29, 194 and assigned to the same assignee as the present invention. The methyl groups of these liquid methyl polysiloxanes are attached to the silicon atom through carbon-silicon linkages.

When a liquid composition comprising a liquid methyl polysiloxane containing an average of about two methyl groups per silicon atom is heated at elevated temperatures (for instance, at 200 to 300 C.) in the presence of air, the liquid polysiloxane will gel after a relatively short period of time. In cases where such liquids are employed, e. g., as lubricating or dielectric media, etc., such a change in properties is highly undesirable. We have now found that the time within which this gelation occurs maybe materially extended by incorporating in the liquid methyl polysiloxane a gelation-retarder comprising ketene. The amount of ketene required is very small. Thus, by weight, we may employ from about 0.05 to about 4 or 5 per cent ketene based on the weight of the liquid methyl polysiloxane. Preferably, we employ from about 0.5 to 2 per cent ketene. No particular advantage is obtained by using more than 5 per cent.

Various methods may be employed to introduce the ketene into the polysiloxane. One method comprises bubbling the ketene gas through the liquid methyl polysiloxane for a period ranging, for example, from about 30 minutes to six or more hours, depending on the degree saturation desired oi the liquid methyl polysiloxane. Additional retardation against gelation may be obtained by removing from the ketene-treated liquid methyl polysiloxane volatile materials boil 1 below ib0 C.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

Example 1 A liquid dimethyl polysiloxane, i. e. a liquid methyl polysiloxane containing an average of about two methyl groups per silicon atom, was prepared by hydrolyzing one liter of dimethyl dichlorosilan in about four liters of water. The oily layer was separated from the aqueous layer, washed several times with water to remove traces of acid, filtered and dried.

The above-prepared liquid methyl polysiloxane was treated with ketene by bubbling the latter A liquid dimethyl polysiloxane was prepared by hydrolyzing substantially pure dimethyl dichlorosilane in water as was done in Example 1. The

oily layer was washed several times with water to remove traces of hydrochloric acid present in the liquid polysiloxane. The liquid polysiloxane was allowed to remain at room temperature for several days. Ketene was bubbled through a sample of this liquid polysiloxane for about 4 hours.

A portion of the ketene-treated oil was distilledto remove all volatile matter boiling below C. A sample of the latter material boiling above 160 0., together with an untreated sample and a sample of the ketene-treated (but not distilled) oil, were each placed in a 200 C. oven and the time noted when gelation of the samples occurred. The untreated oil gelled in about 46 hours while the ketene-treated, but not distilled, oil gelled What we claim as new and desire to secure by Letters Patent oi the United States is:

1. The method or substantially retarding gelation at elevated temperatures or a liquid methyl polysiloxane containing an average of about two methyl groups per silicon atom, which method comprises incorporating in the said polysiloxane from 0.05 to 5 per cent, by weight, ketene based on the weight of the said polysiloxane.

2. The method 01 substantially retarding gelation at elevated temperatures of a liquid methyl polysiloxane containing an average of about two methyl groups per silicon atom, which method comprises (1) incorporating in the said polysiloxane, from 0.05 to 5 per cent, by weight, 15

containing an average of about two methyl groups per silicon atom, said methyl groups ,being attached to the silicon atom through carbon-silicon linkages and (2) from 0.05 to 5 per cent, by weight, ketene based on the weight of the said liquid polysiloxane.

CHARLEB A. BURKHARD. WINTON I. PATNODE.

REFERENCES CITED The following references are of record in the file oi this patent;

UNITED STATES PATENTS Number Name Date 2,389,802 McGregor et a1. Nov. 27, 1945 2,389,803 1 McGregor et al. Nov. 27, 1945 2,389,804 'McGregor et al Nov. 27,1945 2,389,805 McGregor et a1. Nov. 27, 1945 2,389,806 McGregor et a1. Nov. 2'7, 1945 McGregor et'al. Nov. 27, 1945 

